Treatment of wells



Patented Dec. 17, 1935 UNITED STATES 2,024,718 PATENT OFFICE.

2,024,718 TREATMENT or WELLS Leonard C. Chamberlain, Midland, Mich,assignor to The Dow Chemical Company, Midland, Mich, a corporation ofMichigan No Drawing. Application March 14, 1934,v Serial No. 715,475

11 Claims. (01. 166-21) into the surrounding earth or rock by theapplication of fluid pressure. After the acid is neutralized as a resultof its action upon the acid-, soluble constituents of the earthformation, the spent acid is withdrawn from the well. I have observed,however, that in some cases the spent acid can be withdrawn out of theearth formation with dlmculty, or not at all even though the well be putunder vacuum by long continued pumping. When this occurs, the spent acidholds back the oil or gas behind it, so that resumption of production isslow or cannot be had at all.

I have found that the cause of such difficulties seems to be due largelyto the fact that the capillary pores of the earth formation becomefilled with both gas and liquid, thereby giving rise to a phenomenonwhich is similar to, if not identical with, what is known as the J aminaction". The Jamin action may be demonstrated readily in a capillarytube, the surface of the bore of which bears a slight oil film or is notentirely clean, by introducing into such bore alternately a globule ofaqueous liquid and a bubble of gas, so as to form a chain of liquidglobules separated by gas bubbles. Jamin discovered that if the bubblesin such a chain be sufliciently numerous, very high pressures arerequired to force the chain out of the tube. A report of Jaminsexperiments is found in Compt. Rend., vol. 50, 1860, Pp. 172-176,311-314, and 385-389. The magnitude of the pressure required todischarge the chain of alternate liquid globules and gas bubbles fromthe tube depends upon the following factors: (1) the diameter of thecapillary bore, (2) the surface tension of the liquid in contact withthe gas, (3) the degree of adhesion between the liquid and the walls ofthe tube, 1. e. the ability of the liquid to wet the bore of the tube.

The above effect may be produced in an oilbearing sand, the surface ofthe particles of which are more or less coated with oily material. Theinterstices between the particles act like capillaries, and when gas ispresentor is formed therein, as by the action of acid upon a carbonateconstituent of the sand to produce carbon dioxide, a mixture of gasbubbles and liquid droplets is formed in the passages which produces theJamin action and requires a high pressure to force the gas and liquidout'of the capillaries. If the rock pressure does not exceed thatnecessary to overcome the resistance to flow caused by the Jamin action,the aqueous solutions resulting from an acid treatment cannot bedischarged from the well and the same may be sealed permanently thereby.Thus'the usualacid treatment in such a case may result either in sealingthe well permanently against further production or in so greatlyreducing the rate of production as to make operation economicallyimpractical.

The problem of bringing about a resumption of production of a well underthe aforementioned circumstances involves, therefore, reducing thepressure necessary to cause a flow of aqueous 1 solutions through theinterstices of the earth .or rock formation toward the well. For thisthe usual treatments do not provide;

Of the three factors previously enumerated which determine the magnitudeof the resistance 15 to flow resulting from the Jamin action only thesurface tension and adhesion are susceptible of direct control in thetreatment. Since the degree of adhesion between the oil covered earthparticles and the spent acid depends upon the surface tension of thelatter, lowering its surface tension also reduces the degree of adhesionand consequently the Jamin action. On the other hand, merely reducingthe degree of adhesion without substantially reducing the surfacetem' 25sion of the spent acid such as by the use of colloidal solutions inflooding processes does not suffice to overcome the effect of the Jaminaction. This is dueto the fact that the range of action of the adhesiveforces is practically limited to the contacting surfaces. The spent aciddoes not exist in the earth formation as mere tenuous films adhering tooil coated earth particles. It exists as discontinuous portions ofliquid having large enough dimensions to exhibit the properties 35 ofliquids in bulk. In order to reduce the efiect of the Jamin action it isnecessary therefore to substantially change the surface tension of thebulk of the aqueous liquid involved by dissolving therein a. sufiicientquantity of a soluble surface tension lowering agent.

Among the objects of the invention is to provide a method of treatingwells with an acid whereby the porosity of the surrounding earth may beincreased and the rate of production thereby improved with reduced riskof closing the pores of the producing stratum with alternating bubblesof gas and globules of spent acid or aqueous liquid which would preventthe resumption of production. Other objects and advantages will appearas the description proceeds.

My invention is predicated upon the discovery that the tendency foraqueous solutions, and more particularly the spent acid, to remain inthe earth formation-and obstruct or hinder the resumption of productionmay be overcome or at least substantially reduced by incorporating withthe solution a water-soluble agent capable of substantially lowering thesurface tension of aqueous solutions. For example, I have found that,when water-soluble liquids having a lower surface tension than water, aswell as soluble solids whose aqueous solutions possess a lower surfacetension than water, are added to the acid used for treating the well,they are effective to reduce the pressure required to overcome the headcreated by the Jamin action. It is possible by employing such liquids orsolutions in admixture with acid to treat successfully wells in whichthe rock pressure is too low to discharge the spent acid after theconventional acid treatment.

The invention, then, consists of the method hereinafter fully describedand particularly pointed out in the claims, the following descriptionsetting forth in detail certain modes of carrying out the invention,such modesillustrating, however, but various ways in which the principleof the invention may be used.

Broadly stated, the treatment contemplated by my process comprisesintroducing into the earth formation surrounding the well, in connectionwith an acid treatment thereof, a suflicient quantity of an agentcapable of lowering the surface tension of the aqueous solutionresulting from the action of acid upon acid-soluble constituents of theformation, so that the head created by the Jamin action is reduced to apoint where the rock pressure will overcome the same. Agents that lowerthe surface tension of aqueous solutions of calcium or magnesium saltsare effective to lower the surface tension of the spent acid solutionresulting from the aforementioned acid treatment. Such agents also willlower the surface tension of water. However, the choice of such agentmust be restricted to those which dissolve in the spent acid without theformation of a precipitate with salts present in the solution, generallycalcium and magnesium salts. The

proportion of such agent that is most effective to lower the surfacetension is that which forms a saturated solution with water or the spentacid, while proportions lower than the saturating amount have acorrespondingly lesser effect.

The following substances are illustrative of agents suitable for thepurpose: water-soluble alcohols such as methyl, ethyl, normalandisopropyl-alcohol; allyl alcohol; normal-, primary-,, andsecondary-butyl alcohol; primary and tertiary butyl alcohol; normal,iso-primary and active secondary amyl alcohol, tertiary hexyl alcohol;tertiary hexyl phenol; hexyl resorcinol; tertiary butyl catechol;ethylene glycol; watersoluble ketones, such as acetone and methyl ethyl.

ketone; water-soluble ethers, such as dimethyl, methyl ethyl ether,para-hydroxy phenetole; water-soluble aldehydes, such as acetaldehyde,propionic, and normal butyric aldehyde; the water-soluble halogenderivatives of all of the above may be used; water-soluble aliphaticacids, such as valeric, propionic, and butyric acid and theirchlor-derivatives, such as mono-, di-, and trichloracetic acid andalpha-chloropropionic acid. Such agents are sufficiently soluble inaqueous solutions of alkali and alkaline earth metal salts to bringabout an eifective degree of lowering of the surface tension thereof.

The agent and the acid may be mixed together before their introductioninto the well or may be introduced thereinto separately. It is generallypreferable to make a mixture of the acid and the surface tensionlowering agent, so that the latter may be introduced into the well in asingle operation, although if desired the agent may be introduced intothe well ahead of the acid, in which case they may become mixed togetherwithin the earth formation.

In carrying out the treatment of a well, oil and water standing thereinmay be removed if desired by bailing, pumping or the like and then after5 removing the pump, pump rods, and standing valve, if such are there, apredetermined amount of acid is introduced into the well, the amountbeing dependent'uponthe particular well under treatment and may bevaried to suit conditions peculiar to it. It has been found that asuitable charge may be from 1500 to 10,000 pounds or more of the acid.The amount of surface tension lowering agent employed may be from 3 or 5per cent up to 25 or 50 per cent or more of the weight of the acidcharge, depending upon the solubility of the same in the resultingspent-acid and the degree of reduction of the pressure head resultingfrom the Jamin action thereofthat is desired. Water soluble alcohols,such as methyl, ethyl, and isopropyl alcohol, on account of theirrelatively low cost may be employed preferably. For example, 500 gallons(4500 lbs.) of 15 per cent hydrochloric-acid solution (1.075 sp. gr. and50 gallons of ethyl alcohol (330 lbs.) may be employed. Another exampleof a suitable mixture is that formed from l000 gallons vof hydrochloricacid (9000 lbs.) and 200 gallons (1290 lbs.) of isopropyl alcohol.

A suitable charge of acid and surface tension lowering agent such asgiven in the previous ex= amples by way of illustration is introduceddi-i rectly intoa well in any convenient manner, as by pumping throughthe well tube. In order to extend its action beyond the immediatevicinity of the well bore, pressure nay be applied to the acid mixture,for example, by means of gas introduced into the well under pressure orby filling the well bore with oil or water, so as to create ahydrostatic head upon the charge. A convenlent method for introducingthe solution of acid and surface tension lowering agent, that insuresforcing the charge into the earth surrounding the base of the well, isdescribed in U. S. Patent No.

Any acid capable of attacking and dissolving the earth formation so asto form water-soluble salts therewith and increase its porosity may beemployed. Hydrochloric acid is generally suitable for the purpose. Foruse in contact with metal pipes and other parts of well equipment itisbest to add an inhibitor to the acid, as described in U. S. Patent No.1,877,504. A suitable concentration is between 5 and 25 per cent of HCIby weight, although other concentrations may be used, if desired, towhich from 0.5 to 5 per cent of an inhibitor is added.

After the surface tension lowering agentand acid have been introducedinto the well and the acid has become partly or substantially neutral- 6ized by action upon the acid soluble constituents of the earthformation, the spent acid may be' withdrawn. If the surface tension ofthe spent acid is lowered sufliciently by the presence therein of asurface tension lowering agent,relatively low rock pressures willsuffice to cause a move-'- ment of the, spent acid toward the-well, fromwhich it may be removed readily by pumping, bailing or the like. Sincethe back pressure resulting from the Jamin action-is substantiallyreduced by my treatment, in most instances" a substantially completewithdrawal of spentacid maybe had so that the production of oil may beresumed soon after a treatment. I have found also hat the l producedimmediately following a treatment is usually not contaminated with spentacid as is frequently the case in prior methods of treatment.

The effect of water soluble surface tension lowering agents on the headrequired to overcome the Jamin action has been ascertainedexperimentally by the use of a capillary tube having a bore 0.33 mm. indiameter. In these experiments the solution to be tested was introducedinto the bore as drops of solution alternately with bubbles of airthereby forming a Jamin chain therein. Any convenient number of dropsmay be introduced into the tube. Air was then forced into one end of thetube, the other being open, and the air pressure required to force thechain out of the tube was ascertained with a mercury manometer.

It was found that so long as each liquid drop was large enough tocontact the surface of the bore, that is, form a closure therein, thepressure required to force the drops along the bore was independent ofthe lengths of the drops and directly proportioned to the number ofdrops in the chain. By dividing the pressure required to force a chainout of the tube (expressed in centimeters of mercury) by the number ofdrops in the chain, the pressure required per drop is obtained, whichvalue serves to compare the head required to overcome the Jamin actionof various liquids; In the case of aqueous liquids that are ordinarilyfound in Wells such as water, solutions of calcium, magnesium and sodiumchloride and the like of various concentrations, as well as acids.

formerly used to treat a well, the pressure head per drop is betweenabout 0.28 and 0.48 cm.

The reduction in the Jamin pressure head that can be had in my processmay be shown by comparing the pressure required to overcome the Jaminaction of aqueous calcium chloride solution resulting from the action ofsay 15.2 per cent hydrochloric acid on limestone with the pressurerequired with the solution resulting when alcohol is first added to theacid. Aqueous hydrochloric acid containing 15.2 per cent of hydrochloricacid forms 20.7 per cent calcium chloride solution on being neutralizedby acting upon limestone. The pressure required to overcome the Jaminaction of this solution is about 0.3 cm. per drop in a capillary tubehaving a bore of 0.33 mm. If alcohol be added to the acid before actingupon limestone in amount say as given above in the illustrative examplesof suitable acid mixtures, then on neutralizing the acid withlimetstone, the solutions resulting contain 21.3 and 18.2 per cent ofcalcium chloride and 7.0 and 11.5 per cent of ethyl and iso-propylalcohol respectively. The pressure now required to overcome the Jaminaction of these neutralized solutions is only 0.067 and 0.0021 cm.,respectively, per drop in the same capillary tube. Thus the reduction inpressure required to overcome the Jamin action is reduced about 80 percent and 99 per cent, respectively, as a result of the presence ofalcohol in the spent acid.

Other equally striking reductions in the Jamin pressure head may be hadby dissolving*a suitableamount of a soluble surface tension loweringagent in the liquid involved. Tests of the kind described also furnish aguide in selecting the amount and kind of agents for the purpose andgives a means for distinguishing operative agents from those that do notbring about a reduction in the Jamin pressure head. Colloidal inventionmay be employed instead of those explained, change being made as regardsthe method 10 herein disclosed, provided the step or steps stated by anyof the following claims or the equivalent of such stated step or stepsbe employed.

I therefore particularly point out and distinctly claim as myinvention:- 15 1. In a method of treating a well, the steps whichconsist in introducing thereinto a. watersoluble agentcapable ofsubstantially lowering the surface tension of water and an acid capableof forming water-soluble salts with the earth for- 20 mation.

2. In a method of treating a well, the step which consists inintroducing thereinto an aqueous solution of an agent capable ofsubstantially lowering the surface tension of water and an acid 2capable of forming water-soluble salts'with the earth formation.

3. In a method of treating a well, the steps which consist in forming asolution of an acid capable of producing water-soluble'salts with the 30earth formation and an agent, soluble in said acid, capable ofsubstantially lowering the surface tension of water, and introducing theso formed solution into a well.

4. In a method of treating a well, the steps 35 which consist inintroducing thereinto an acid solution capable of forming water-solublesalts with the earth formation, to which solution is added from 3 to percent of a water-soluble alcohol.

5. In a method of treating a well, the step which consists inintroducing thereinto an aqueous solution of hydrochloric acid and analcohol selected from the group consisting of methyl alcohol, ethylalcohol, normal'and iso-propyl alcohol and butyl alcohols.

6. In a method of treating a well to increase the output therefrom, thesteps which consist in introducing thereinto an acid capable of formingwater-soluble salts with the earth formation and 50 a water-solubleliquid agent having a lower surface tension than water.

7. In a. method of treating a well to increase the output therefrom, thesteps which consist in introducing thereinto an acid capable of formingwater-soluble salts with the earth formation and a water-soluble liquidagent capable of lowering the surface tension of water.

8. A method of treating a well which comprises introducing thereinto awater-soluble alcohol and hydrochloric acid.

9. In a process of cleaning wells the step comprising charging thereintoa. composition comprising inhibited hydrochloric acid and N-butylalcohol.

10. In a process of cleaning wells the step comprising chargingthereinto a composition comprising inhibited hydrochloric acid andacetone.

11. In a process of cleaning wells the step comprising chargingthereinto a composition comprising inhibited hydrochloric acid and ethylalcohol.

' 1 LEONARD C. CHAMBERLAIN.

